### Downwind Sails Test Case (AC33 Asymmetric Spinnaker)

Summary of available data:

- Forces
- Surface pressures
- Numerical simulation (Detached Eddy Simulation)

#### Data

A flexible and a rigid 1:15th-scale model of an AC33-class yacht were tested in the Yacht Research Unit wind tunnel at the University of Auckland. Forces and surface pressures were measured. The tested geometry is:

The measurements were presented in the following papers.

Pressure measurements on the rigid model and comparison with previous measurements:

Pressure measurements on the flexible model and comparison with other sails:

Force measurements on the flexible model and comparison with other sails:

Numerical simulation (Detached Eddy Simulation) of the wind tunnel tests:

Videos of the numerical simulations can be downloaded here. If you want to use these videos, please acknowledge the authors as “Courtesy of Viola et al., 2014, Ocean Eng., 90:93-103”.

### Upwind Sails test case

Summary of available data:

- Surface pressures
- Numerical simulation (Reynolds-averaged Navier-Stokes)
- Guidelines and example of verification and validation of Reynolds-averaged Navier-Stokes simulations
- Questions and answers

#### Data

A rigid 1:15th-scale model of an AC33-class yacht was tested in the Yacht Research Unit wind tunnel at the University of Auckland. Forces and surface pressures were measured. The sails were supported with wind-transparent fishing lines, and a flat plate was used to model the boat deck. Four genoa and four mainsail trims were tested varying the sheet angle, resulting in 16 test conditions. Four twist of the mainsail and three twist of the genoa were also tested, resulting in 7 additional trims. The geometry of the sails, the pressure coefficients along four horizontal sections of each sail, the results of the numerical simulations and a full verification and validation of the computed pressure distributions are provided herein.

Description of the experiments and results:

Table of the pressure coefficients:

Sail geometries:

Numerical simulations (Reynolds-averaged Navier-Stokes) of the wind tunnel tests:

Verification and validation of Reynolds-averaged Navier-Stokes simulations:

**Q:** Geometry: 4 positions of the genoa and of the mainsail in the IGES. With respect to your paper in which you mention G#M#, we would like to know the relation between these numbers # and the positions in the IGES file.

**A:** The notation G#M# uses 1 as the tightest trim (highest angle of attack) and 4 for the loosest trim (lowest angle of attack).

**Q:** Boundary conditions: to your opinion, what is the best boundary condition to use for the computation on the bottom plane of the computational domain? Slip or No-Slip? In the experiments, is the boundary layer very thick at the location of the sails?

**A:** I suggest to use a non-slip condition on the bottom plane. However I guess that the lower face of your domain will be larger than the bottom plane so you will need to decide what to do elsewhere. Elsewhere I suggest non-slip. If you want to make it more complicated but possibly more accurate, you can take some ideas from Viola et al., 2012 where we performed two simulations: the first simulation provided the boundary conditions for the second one.

**Q:** Inlet conditions: from the Reynolds 2.3E05 given in the paper, (using averaged chord c=0.49m), we deduced that the inlet velocity is about 7.1 m/s. Is this a correct value to prescribe at the inlet?

**A:** The Reynolds number was based on the model height h=2.3m, the dynamic pressure was 32.5 ± 1 Pa and the free stream turbulence intensity was 3%.